1. Field of the Invention
This invention relates to a flow controlling method for an auxiliary intake flow passage for controlling the flow rate of air to flow through an auxiliary intake flow passage in a power unit wherein a main intake flow passage and the auxiliary intake flow passage are communicated with an engine and a starter clutch such as a centrifugal clutch is disposed between the engine and a transmission.
2. Description of Background Art
A configuration which includes, in addition to a main intake flow passage on which a throttle valve is disposed, an auxiliary intake flow passage on which an intake air control valve (IACV) is disposed is known. See, for example, Japanese Patent Laid-Open No. 2005-105938 and Japanese Patent Laid-Open No. Sho 62-195430. With such a configuration as just described, even in a state wherein a throttle valve whose opening varies in response to an acceleration/deceleration operation of a driver is closed to a predetermined opening, since an ECU (electrical control unit) controls the opening of the IACV, stabilization of the engine speed upon idling and enhancement of the engine start ability in a low temperature state are achieved.
In Japanese Patent Laid-Open No. 2005-105938, when the engine is in an idling state, feedback control for controlling an IACV so that the actual engine speed may coincide with a target engine speed is used, but when the engine is in a non-idling state, open loop control of controlling the IACV based on the temperature of engine cooling water is used. See, the abstract of Japanese Patent Laid-Open No. 2005-105938. A decision between the idling state and the non-idling state is carried out based on whether the throttle opening is lower than an opening at which the throttle is open a little from the opening in a fully closed state and whether or not the engine speed is lower than a speed of rotation which is a tittle higher than the idling speed. See, paragraph [0015] of Japanese Patent Laid-Open No. 2005-105938.
In addition, a starter clutch (for example, a centrifugal clutch) which is engaged and disengaged automatically in response to the engine speed in order to implement smooth starting and stopping and so forth is known. See, FIG. 9 of Japanese Patent Laid-Open No. 2006-200727.
While an IACV is disclosed in Japanese Patent Laid-Open No. 2005-105938 and Japanese Patent Laid-Open No. Sho 62-195430 and a starter clutch is disclosed in Japanese Patent Laid-Open No. 2006-200727, a method of causing an IACV to operate suitably in a power unit which includes an IACV and a starter clutch (method of suitably controlling the flow rate of air to flow through an auxiliary intake flow passage) has not been investigated.